The afferent and sympathetic components of the lumbar spinal outflow to the colon and pelvic organs in the cat. III. The colonic nerves, incorporating an analysis of all components of the lumbar prevertebral outflow.

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project to the colon along the inferior mesenteric artery of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons. The numbers, segmental distribution, location, and size of these labeled somata have been determined quantitatively. Afferent cell bodies were symmetrically distributed bilaterally in dorsal root ganglia T13-L5, with the maximum number (about 80%) in L3 and L4 and most of the rest in L2. Labeled afferent somata were small relative to the entire population of DRG cells. Occasionally a few preganglionic somata were labeled in the intermediate zone of L3 and L4 spinal cord segments. Postganglionic cell bodies were labeled bilaterally in the proximal lobes of the inferior mesenteric ganglion (70-95%), in accessory ganglia of the intermesenteric nerve and of the lumbar splanchnic nerves, and in lumbar paravertebral ganglia. The segmental distribution in the lumbar sympathetic trunk was symmetrical on both sides and was the same as that of the afferent cells. Labeled postganglionic cell bodies in both the IMG and the accessory ganglia were larger than labeled and unlabeled ganglion cells in the paravertebral ganglia. From these data, it is estimated that about 2,100 afferent neurons and about 29,000 postganglionic neurons project in the lumbar colonic nerves. In conjunction with equivalent data for the hypogastric and lumbar splanchnic nerves, the results provide a quantitative and spatial description of the afferent and efferent components of the lumbar innervation of the colon and pelvic viscera.